In a wireless communication system that supports a device-to-device discovery, discovery information is transmitted by user equipment (UE) that desires to be discovered. Such discovery information is transmitted on a discovery physical channel by UE. The discovery information is formed of an application user ID and any other information which receiving UE has interest in. Based on received discovery information, discovering UE determines whether other UE has interest in it. If proximity of UE needs to be known by one or more licensed applications in discovering UE, UE has interest in discovering ProSe-enabled UE. ProSe discovery may be, for example, a standalone service enabler that can use information from UE discovered with regard to specific applications. In this case, specific applications may be allowed to use such information, e.g., “find a taxi nearby” or “find me police officer X”. Additionally, ProSe discovery obtained according to such information may be used, for example, in the following operation for triggering direct communication.
In a current system, discovery information transmitted by UE may be received by any other UE authorized to monitor a discovery physical channel. Such discovery information is transmitted by UE authorized for transmission. However, such discovery information is transmitted through a broadcast channel, and a discovery resource is not allocated to specific UE for transmission. In a certain case, even though a discovery resource may be allocated to specific UE for transmission, receiving UE does not know a specific discovery resource used by a transmitter. Discovery information transmitted by UE may be received and processed by any UE (in case of open discovery) or by a specific group of UE (in case of limited discovery).
In the above-type many-to-many communication on a discovery physical channel, discovery information may fail to be transmitted safely. Rogue UE may receive a discovery protocol data unit (PDU) transmitted on the discovery physical channel. Also, rogue UE may store the discovery PDU and transmit it onto the discovery physical channel. This may cause wrong information reception to UE receiving the discovery PDU transmitted by rogue UE. For example, pizza shop UE may signal an offer at specific time. When there is no offer, rogue UE may replay this message. In another example, rogue UE may replay a discovery signal of a user's friend. Due to this, even though a user's friend is not actually located nearby, a user may think a friend is located nearby. Therefore, a mechanism for replay protection should be provided to secure discovery information.
The discovery capability of a discovery physical channel is small. Therefore, the replay protection mechanism should minimize overhead. Currently the replay protection mechanism uses a counter or packet number. If transmission can be received by any UE, the counter or packet number cannot be maintained. Also, UEs that receive transmission may be varied according to time. In this case, it is not possible to have the counter or packet number synchronized between a transmitter and a receiver. A certain replay protection mechanism proposes using a system time such as hour, minute, second, or any other equivalent. However, it is not possible to always have such a system time synchronized through a transmitter and a receiver. Additionally, in case any applied system time is delivered to discovery information, a system time approach scheme may require further overhead. Most systems are synchronized in time by using their mechanism such as dividing time in a view of frame. For example, in some systems, a frame duration time is 10 ms, and a transmitter and a receiver are synchronized with frame boundaries. A frame is numbered and quickly rolls over. For example, a ten-bit frame number rolls over at every ten seconds. It is not desirable to use a frame number for a replay protection since a security key to be updated at every 10 seconds is needed. Some methods use a frame number and a rollover counter in order to reduce the frequency of a security key update. The rollover counter needs to be transmitted together with discovery information so that a transmitter and a receiver are synchronized with each other. This, however, increases overhead. Furthermore, discovery information is transmitted by several UEs and received by several UEs. It is not possible to use a rollover counter synchronized with all UEs.
Accordingly, a method for securing discovery information is required.